Anatomy of the Pulsating Double Layer Source in the Earth's Magnetotail

Abstract

This investigation is composed of an observational part, plus a new theoretical model interpreting the related exhibited satellite datasets through an entirely new approach concerning the substorm's ultimate excitation mechanism. First, we present a few representative case studies showing the B z component of the magnetic field to develop quasi-periodic negative deflections with periodicities ranging from T=15 to 60s in the central plasma sheet (CPS) with persistent tailward plasma flows. The wave activity of B z is much lower outside the CPS, while occasionally almost a monochromatic response is identified. In certain cases, a profound change of frequency is evident and happens most probably due to the Doppler-effect; there is a relation between the plasma velocity enhancement and the increase of frequency. When comparing the amplitude of Bz deflections to the lobe magnetic field, one plausibly may infer that the deflections reflect the very dynamics of the source itself. Therefore, we put forward the concept about "a pulsating source", and more specifically, we adopt the pulsating "twin Double Layer (DL) structure" as the ultimate mechanism converting magnetic energy to kinetic. The DL acts either as a resistor or a capacitor and the twin-DL structure approximately behaves in a way similar to the cardiac cycle with repeated, rhythmic contractions and expansions. The contraction phase represents the abrupt local thinning of the plasma sheet (PS) that terminates explosively, heating the plasma and accelerating energetic particles. The expansion phase corresponds to a local distention of the source, which also terminates explosively. The DLs are oppositely polarized depending on the range of Rc whether it fulfills the condition r gi ≤ R c < 9 r gi or r ge < R c < r gi , where r gi (r ge) and R c are the ion (electron) gyro-radius and the curvature radius of the local magnetic field, respectively. In more detail, the "akis structure", as it was earlier introduced by Sarafopoulos [1, 2] and further elaborated in this work, repetitively forms DLs that undergo a transition from depolarization to repolarization in each of the consecutive cycles. The collapse of the dissipation region (leading to local dipolarization) seems to occur when r ge < Rc < 9r ge. Large scale Boström's type II field aligned currents (FACs) flow and neutralize the net charges produced by "charge separation processes" within the twin-DL structure; thus the whole structure principally operates (under favorable conditions) like a huge resonant RLC-type circuit. Actually the pulsating source is an integral part of that huge (resonating) circuit, wherein even the ionosphere obviously plays its vital role imposing a positive feedback. The author of this study believes that Faraday's law can be experimentally validated with his suggested model more reliably than with the alternative X-type magnetic reconnection model incorporating the concept of "magnetic diffusion". The presently proposed "akis structure" embedded in the whole magnetotail's current sy...

The Pattern of By Deflections Produced from Field-Aligned Currents Earthward of the Activation Source in the Earth’s Magnetosphere

“…Simulations supporting the latter concept are performed by Sarris and Li [32]. The concept underlying this work may be distinguished from the others in that the populations are essentially energized at the source site by a specific mechanism, for instance, the explosive phase of the twin Double Layer (DL) structure, as we already suggested [11]. According to the Double Layer model, the resulting ion particles are going to build the B z dipolarization front.…”

“…In the context of a hypothetically pulsating source, which was studied in detail by Sarafopoulos [11], one would probably identify successive and quasi-periodic activation episodes, while the tail repetitively recovers its more dipole-like structure through successive-distinct dipolarization fronts. Unavoidably, in each front, the B y deflection (with the appropriate sign) interrelates with each B z increase; in addition, the satellite will most likely move inward (given that the tail inflates) while detecting earthward fluxes.…”

“…For only 500 eV electrons the ratio of convection to ballistic velocities will be ~1/7. In our view, a more pragmatic approach would be as follows: First, the electrons and ions are accelerated in the same manner at the source region (S) simultaneously by a mechanism associated with the "twin-Double Layer structure" in its explosive phase, as proposed by Sarafopoulos [11]. Then, both electrons and ions move outward from the source, with the difference that the electrons are apparently going to become adiabatic just outside the EDR (green rectangle in Figure 10), whereas the ions will become adiabatic just outside the IDR (blue rectangle for the same figure).…”

“…If an IDR is locally established in tail, then the ions will cease drifting earthward within this region; consequently, a net earthward electron flow will be established. Furthermore, the IDR will become a cavity with increased charge densities (for both charge carriers); and such a cavity potentially leads to the "twin-DL structure" with repetitive activations as suggested by Sarafopoulos [11]. And the DLs would convert the magnetic energy into mechanical one and readily produce energetic particles.…”

“…We assume that the demagnetized ions, in a thinned plasma sheet (PS), have the potentiality to stream outward from the source while moving within "an ion channel" within the IDR and along the tail in central plasma sheet (CPS). A mechanism generating these "ion jets" was proposed by Sarafopoulos [10] [11] based on a twin-Double Layer (twin-DL) structure, and more specifically, on its phase of explosive activations. In this work, each earthward ion jet is associated with ion FACs formed outside the IDR and producing the studied B y deflection pattern.…”